1. Field of the Invention
The present invention relates to a film scanner for scanning an image formed on a silver halide film by a photoelectric conversion element to convert it to an image signal.
2. Description of the Related Art
Recently, along with the development of personal computers (PC), it is known that an image taken by a digital still camera and an image scanned by a scanner are input into a PC for image processing or storage. Similarly, an image, recorded on a photographic film such as silver halide film, can be scanned by the scanner and input into the PC. In the scanner, a line sensor comprised of an array of photoelectric conversion elements is moved in a sub-scan direction perpendicular to the longitudinal direction of the line sensor.
In this type of film scanner, it is desired to scan the film image at different resolutions. For example, when dense image data is desired, the image is scanned at a high resolution, while when the PC has a small storage capacity, the image is scanned at a low resolution. Alternatively, there are scanners provided with pre-scan functions of scanning a film image at a low resolution for confirmation before the main-scan of the film image at the regular resolution. In such a case, normally, the pitch by which the film is transported for scanning the film image at different positions is changed. For the high resolution main-scan, the pitch of the film transport is made fine, while for the low resolution pre-scan, the pitch of film transport is made coarse. Therefore, conventionally, provision has been made for a stepper motor serving as the source of drive power for the transport mechanism which moves the transport table and a variable speed reduction mechanism to switch the rotational output of the stepper motor. A predetermined pulse is supplied per unit time to the stepper motor to drive the rotation of the stepper motor in predetermined steps. In the main-scan and the pre-scan, the speed ratio of the speed changer is switched to change the pitch of movement of the transport table.
In a film transport mechanism of such a configuration, however, a gear mechanism comprised of a plurality of gears is required for constructing the variable speed reduction mechanism used as the speed changer. Further, a mechanism is necessary for switching the states of engagement of the plurality of gears to change the speed ratio. Thus, the film transport mechanism becomes complicated. This becomes an obstacle in reducing the size and cost of the film scanner. Further, it may be considered to set the scanning pitch of the film transport mechanism at the minimum pitch and switch the number of pulses for driving the stepper motor so as to change the pitch of movement of the transport table between the main-scan and the pre-scan, but the number of pulses supplied to the stepper motor itself would be the same between the pre-scan and the main-scan, so the pre-scan would then take the same degree of time as the main-scan despite the coarse scan.